Antennas for transmission and reception need to provide high fidelity information on the nature of the signals received or transmitted. These signals can be distorted in a number of ways, including by the design of the antenna, through its frequency band of operation, and by the manner in which the antenna may be mounted. In addition, signal distortion may be caused by the materials from which the antenna is made. For instance, the materials from which the antenna is made may cause phase distortion. Phase distortion is typically frequency dependent and can be set up by surface currents induced in conductors by high frequency AC fields. However, the resistance provided by such materials is usually isotropic in nature. As a result, the signal is attenuated along the length of the antenna, as well as across the narrow diameter of the antenna.
The materials from which the antenna is made may also give rise to the occurrence of surface currents. Typically, surface currents can be inducted in high frequency transmission of information. The presence of surface currents can lead to frequency related phase shifts with the potential to distort or degrade transmitted information.
The materials from which the antenna is made can further enhance the thermal signature of the antenna. In particular, the material used can affect the resistivity and limit the current carrying capacity in the antenna. As a result, when a relatively high amount of currents is being carried along the antenna, the antenna may heat up, thereby increasing the thermal signature of the antenna. Such enhancement in the thermal signature, under most circumstances can be undesirable and the thermal energy expended is a waste of power.
It is believed that carbon nanotubes may have properties that potentially can overcome these problems and further offer the promise of much higher power radiated per input power. Nanotubes have been known for some time. Examples of literature disclosing nanotubes include, J. Catalysis, 37, 101 (1975); Journal of Crystal Growth 32, 35 (1976); “Formation of Filamentous Carbon”, Chemistry of Physics of Carbon, ed. Philip L. Walker, Jr. and Peter Thrower, Vol. 14, Marcel Dekker, Inc, New York and Basel, 1978; and U.S. Pat. No. 4,663,230, issued Dec. 6, 1984. More recent interest in carbon filamentary material was stimulated by a paper by Sumio Iijima in Nature 354, 56 (1991) also describing synthesis and structure of carbon nanotubes. These early studies and the work that has developed from these studies resulted in a material with remarkable mechanical and electronic properties. However, the nanotubes that these studies produced have been relatively short and can be limited for composite material reinforcement or for spinning into yarns or filaments for use as antennas. In addition many of these early carbon nanotubes were encrusted with amorphous carbon thereby degrading their usefulness.
Present commercial methods for the manufacture of nanotubes can generate only relatively short length nanotubes. Lengths typically may vary from a few nanometers (e.g., 10 nm) to only tens of microns in length. As a consequence, antennas manufactured from these relatively short length nanotubes can result in inefficient conduction from one relatively short nanotube to another. Conduction from short structure to short structure can lead to relatively high resistivity along the length of the antenna, and can also preclude using ballistic conduction potential of these materials. Further, the shorter tubes produce weaker yarns so handling and attaching to this material may be difficult.
Accordingly, it would be desirable to provide an antennas which can minimize signal distortion, including phase distortion, and phase shifts caused by surface currents, minimize thermal signature under very high power, while at the same time providing substantially enhanced conduction.